Longhai Piao

Synthesis of silver nanoplates by two-dimensional oriented attachment.

Synthesis of silver nanoplates was studied in the modified polyol method, where the nucleation and seed stage occurred in a poly(ethylene glycol) (PEG)-water mixture solution, and the growth stage happened in the PEG environment. The morphological evolution of nanoplates was characterized using UV, SEM, and TEM. Interestingly, plane nanostructures with unusual jagged edges were finally formed in our modified polyol method. Using TEM, we observed the medium state of fusion between two nanoplates, resulting in generating unusual jagged edges. Therefore, a novel two-dimensional oriented attachment occurred in our modified polyol method, which involves smaller nanoplates as the building blocks. Further control experiments showed that the presence of water could break this kinetic preferred reactivity, leading to the formation of nanoparticles.

Crystal-to-crystal conversion of Cu2O nanoparticles to Cu crystals and applications in printed electronics

In order to realize copper-based electrode materials for printed electronics applications, it is necessary to control the oxidation reaction during the sintering process. Here we report a novel approach based on the conversion process of cuprous oxide (Cu2O) nanoparticle aggregates (NPAs) to metallic copper crystals. The NPAs undergo crystal conversion to copper crystals in air with the help of surfactants and a reducing agent. This crystal conversion is a very unique phenomenon which has not been observed previously. The detailed mechanism for this conversion, including the role of the surfactant and crystal growth, was proposed. Furthermore, we tried to realize oxidation free copper electrode formation in air by using the crystal conversion of Cu2O NPAs.

Facile synthesis and size control of spherical aggregates composed of Cu2O nanoparticles

The secondary structures of Cu(2)O nanoparticles were prepared in aqueous solution utilizing self-assembled aggregation process. By introducing polyacrylamide (PAM) as a secondary surfactant, the colloidal nanoparticle aggregates (CNAs) become uniform in size and exhibit spherical shape compared to the random aggregates without PAM. The size of CNA can be systematically controlled from 300nm to 1000nm by varying PAM concentration. The formation mechanism was explained based on a conventional colloidal particle formation mechanism. These control methods may generally be applied to the preparation of secondary nanoparticle structures.

Effect of Pluronic block copolymers on aqueous dispersions of graphene oxide

The effect of Pluronic block copolymers F127 and P123 on aqueous dispersions of graphene oxide (GO) was studied. The combination of optical microscopy, rheometry, scanning electron microscopy and X-ray diffractometry studies indicated that the introduction of Pluronics F127 and P123 could markedly change the dispersion, flow and processing behaviors of GO in water. Interestingly, the ordered-lamellar-structure composite tapes were easily fabricated by casting the GO/F127 dispersions through a doctor blade method while they were not obtained by casting the GO/P123 dispersions. The study on the intercalation structure of GO composite tapes suggested that the ordered lamellar structure of GO/F127 composite tapes originated from the anchor-buoy-type adsorption of F127 on the GO surface. In the anchor-buoy-type configuration, long ethylene oxide (EO) segments of F127 were extended out into water to form a hydration protection layer, which effectively prevented the aggregation of GO sheets. Instead, the protective effect was weaker for P123 due to its very short EO segments, and the phase-separated dispersions were present with higher GO content.

Assembling Ag nanoparticles into morphology controlled secondary structures on loosely packed self-assembled monolayers.

An efficient route for the assembling of Ag nanoparticles (NPs) onto solution phase Ag(palmitate) bilayer structure has been developed. Two dimension (2D) arrays of Ag NPs on Ag(palmitate) were prepared by treating palmitate stabilized Ag NPs with the as-synthesized Ag(palmitate) or ribbon-shaped Ag(palmitate) templates. The interaction between long chain carboxylate surfactants of Ag NPs and the protruding aliphatic chains of the loosely packed self-assembled monolayer may play a role in directing the self-assembly of NPs in monolayer fashion. In addition, facile method to control morphology of Ag(carboxylates) from micro-flakes to micro-ribbons was also demonstrated.

High-Performance Stretchable Conductive Composite Fibers from Surface-Modified Silver Nanowires and Thermoplastic Polyurethane by Wet Spinning

Highly stretchable and conductive fibers have attracted great interest as a fundamental building block for the next generation of textile-based electronics. Because of its high conductivity and high aspect ratio, the Ag nanowire (AgNW) has been considered one of the most promising conducting materials for the percolation network-based conductive films and composites. However, the poor dispersibility of AgNWs in hydrophobic polymers has hindered their application to stretchable conductive composite fibers. In this paper, we present a highly stretchable and conductive composite fiber from the co-spinning of surface-modified AgNWs and thermoplastic polyurethane (PU). The surface modification of AgNWs with a polyethylene glycol derivative improved the compatibility of PU and AgNWs, which allowed the NWs to disperse homogeneously in the elastomeric matrix, forming effective percolation networks and causing the composite fiber to show enhanced electrical and mechanical performance. The maximum AgNW mass fraction in the composite fiber was 75.9 wt %, and its initial electrical conductivity was as high as 14 205 S/cm. The composite fibers also exhibited superior stretchability: the maximum rupture strain of the composite fiber with 14.6 wt % AgNW was 786%, and the composite fiber was also conductive even when it was stretched up to 200%. In addition, 2-dimensional (2-D) Ag nanoplates were added to the AgNW/PU composite fibers to increase the stability of the conductive network under repeated stretching and releasing. The Ag nanoplates acted as a bridge to effectively prevent the AgNWs from slippage and greatly improved the stability of the conductive network.

A novel self-seeding polyol synthesis of Ag nanowires using mPEG-b-PVP diblock copolymer

The homopolymer of poly(N-vinylpyrrolidone) (PVP) is typically chosen as a capping agent for the polyol synthesis of silver nanowires (Ag NWs). In this paper, we first introduced methoxy poly(ethylene glycol)-b-PVP diblock copolymer (mPEG-b-PVP), which was synthesized by reversible addition–fragmentation transfer (RAFT) polymerization, as a capping agent instead of the PVP homopolymer to the polyol process. Ag NWs were successfully synthesized by this self-seeding process without the addition of any other additives, such as metal salt or exotic seed. The Ag NWs were analyzed by field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform-infrared spectroscopy (FT-IR). In addition, the relationship between the final morphology of the products and the reaction parameters, such as the molar ratio of mPEG-b-PVP to AgNO3, injection rate, and temperature, were studied. Finally, under the optimum conditions, the Ag NWs, which were nearly uniform in size, measured 60 to 75 nm in diameter and were as long as ∼20 μm. Notably, the synthesized Ag NWs can be dispersed in a non-polar solvent due to the surface PEG tails. This improvement in the dispersion stability may broaden the application of Ag NWs.

Rapid Macroscopic-Scale Assembly of Ag Nanowires at the Water/Air Interface

Rapid macroscopic-scale assembly of Ag nanowires was demonstrated through facile self-assembly at the water/air interface. This self-assembly was induced by heating due to the surface tension effect and convection. Interestingly, a rippled hairstyle superstructure was observed when the aqueous dispersions of thinner Ag nanowires were heated. Applying the Euler buckling theory for a set of aligned Ag nanowires, it was found that the water surface tension was sufficient to bend or buckle these free Ag nanowires trapped between two nanowire stripes, which resulted in the formation of the rippled hairstyle superstructure. However, the formation of the nanowire stripes was driven by steric repulsion of nanowires along with their short-range van der Waals interactions and later lateral capillary attraction between large building blocks. Such control over self-assembly is key for designing hierarchically ordered structures, which opens a new opportunity in the exploration of novel properties and the development of new applications.

Base Effects on Carbonylative Polymerization of Propylene Oxide with a [(salph)Cr(THF)2]+[Co(CO)4]− Catalyst

Poly (3-hydroxybutyrate) (PHB) is a naturally occurring biodegradable and biocompatible polyester and considered as a class of potentially thermoplastic biopolymers in industry. The alternating copolymerization of cheap and available propylene oxide and carbon monoxide may be an efficient synthetic route for PHB. Here, we studied the base effects on the synthesis of PHB using a well-defined [(salph)Cr(THF)2]+[Co(CO)4]− catalyst combined with various bases. It was found that base not only affects the yield of PHB, but also the molar ratio of each unit in the product.

Quantitative analysis of the relationship between the dispersion stability of mixed-surfactant Ag nanoparticles and their composition

Understanding the surfactant layer composition and morphology of metal nanoparticles (NPs) with single-molecule surfactants is crucial for controlling the properties of NPs. Previously, we reported that the dispersion stability of Ag NPs could be greatly enhanced by mixing n-alkyl carboxylic acid surfactants with two different chain lengths. In this paper, we continued this previous study by quantitatively analyzing the relationship between the surfactant shell composition and the dispersion stability of mixed-surfactant Ag NPs. We found that the Ag NP dispersion stability was greatly influenced by the molar ratio and the difference in chain lengths of the surfactants. To obtain a superior dispersion stability, the molar ratio of the two surfactants with different chain lengths should be close to 1 : 1, and the difference in chain lengths should be greater than or equal to four carbon atoms. We also found that the dispersion stability of Ag NPs with a mixed surfactant of palmitic acid (C16) and dodecanoic acid (C12) is insensitive to the type of solvent used.